Class<X> exceptionType,
        AsyncFunction<? super X, ? extends V> fallback) {
      super(input, exceptionType, fallback);
    }

    @Override
    ListenableFuture<? extends V> doFallback(
        AsyncFunction<? super X, ? extends V> fallback, X cause) throws Exception {
      ListenableFuture<? extends V> replacement = fallback.apply(cause);
      checkNotNull(
          replacement,

   *
   * @param future The future attach the callback to.
   * @param callback The callback to invoke when {@code future} is completed.
   * @param executor The executor to run {@code callback} when the future completes.
   * @since 10.0
   */
  public static <V extends @Nullable Object> void addCallback(
      final ListenableFuture<V> future,
      final FutureCallback<? super V> callback,
      Executor executor) {

 * introduces some testing difficulties. This test exercises the two fallback strategies in abstract
 * future.
 *
 * <ul>
 *   <li>SafeAtomicHelper: uses AtomicReferenceFieldsUpdaters to implement synchronization
 *   <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AbstractFuture} (and all of {@code

 *
 * @author Kevin Damm
 * @author Kyle Maddison
 */
@ElementTypesAreNonnullByDefault
final class LittleEndianByteArray {

  /** The instance that actually does the work; delegates to Unsafe or a pure-Java fallback. */
  private static final LittleEndianBytes byteArray;

  /**
   * Load 8 bytes into long in a little endian manner, from the substring between position and

 * and performant but introduces some testing difficulties. This test exercises the two fallback
 * strategies.
 *
 * <ul>
 *   <li>SafeAtomicHelper: uses Atomic FieldsUpdaters to implement synchronization
 *   <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AggregateFutureState} (and all of

 * introduces some testing difficulties. This test exercises the two fallback strategies in abstract
 * future.
 *
 * <ul>
 *   <li>SafeAtomicHelper: uses AtomicReferenceFieldsUpdaters to implement synchronization
 *   <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AbstractFuture} (and all of {@code

   * java.util.concurrent.CompletableFuture#thenAcceptAsync}.
   *
   * @param callback The callback to invoke when this {@code Future} is completed.
   * @param executor The executor to run {@code callback} when the future completes.
   */
  public final void addCallback(FutureCallback<? super V> callback, Executor executor) {
    Futures.addCallback(this, callback, executor);
  }

   *     exception itself.
   * @param executor the executor that runs {@code fallback} if the input fails
   */
  public <X extends Throwable> ClosingFuture<V> catching(
      Class<X> exceptionType, ClosingFunction<? super X, ? extends V> fallback, Executor executor) {
    return catchingMoreGeneric(exceptionType, fallback, executor);
  }

      Class<Throwable> exceptionType,
      Function<? super Throwable, ? extends V> fallback,
      Executor executor) {
    return (FluentFuture<V>) Futures.catching(this, exceptionType, fallback, executor);
  }

  public final FluentFuture<V> catchingAsync(
      Class<Throwable> exceptionType,
      AsyncFunction<? super Throwable, ? extends V> fallback,
      Executor executor) {

  public void testOr_supplier_present() {
    assertEquals("a", Optional.of("a").or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_supplier_absent() {
    assertEquals("fallback", Optional.absent().or(Suppliers.ofInstance("fallback")));
  }

  public void testOr_nullSupplier_absent() {